Which of the following requires the GREATEST RELEASE of latent heat energy into the atmosphere?

All of the following are properties that make water unique among other substances on Earth EXCEPT:

The air in Great Falls, Montana has a temperature of 5°C and a relative humidity of 50 percent. On the same afternoon, the air in Palm Springs, California has a temperature of 25°C and a relative humidity of 50 percent. What can be said about the amount of vapor in the air at these two cities?